There is a trend towards increasingly large passenger aircraft with higher performance efficiency (for example fuel burn reduction). It is desirable for these aircraft to have correspondingly large wing spans, in order to maximise performance efficiency. However, maximum aircraft span is effectively limited by airport operating rules that govern various clearances required when manoeuvring around the airport (such as span and/or ground clearance required for gate entry and safe taxi usage).
To address this problem, various arrangements comprising moveable wing tip devices, that specifically enable the span to be reduced in a ground configuration, have been suggested. US2013/0099060 and WO2015/150816 are examples of moveable wing tip devices in which the wing tip device is moveable about a hinge. In another arrangement, shown in WO2015/150835, the wing tip device and the fixed wing are separated along an oblique cut plane, and the wing tip device is rotatable about an axis of rotation perpendicular to the cut plane.
In these designs, the wing tip device is configurable between: (i) a flight configuration for use during flight and (ii) a ground configuration for use during ground-based operations, in which ground configuration the wing tip device is moved away from the flight configuration such that the span of the aircraft wing is reduced. In the flight configuration, the wing tip device tends to be an extension of the outer part of the fixed wing, and the span typically exceeds an airport compatibility limit (such as a gate limit). In the ground configuration the span is typically reduced such that the span (with the wing tip device in the ground configuration) is less than, or substantially equal to, the airport compatibility gate limit.
The wing tip device in the flight configuration tends to be arranged to provide acceptable performance during a range of flight conditions (e.g. cruise, climb and take-off/landing). In order to provide acceptable performance across this range of conditions, the performance in each specific flight condition necessarily tends to be sub-optimal.
The present invention seeks to mitigate at least some of the above-mentioned problems.